Process for the continuous production of cellulose esters



R.YCLEVY ET AL Jan. 22,1957

Filed March 13, 1953 INVENTORS= ROLAND CLEVY JEAN ROBIN A BY ATTORNEY PROCESS FOR THE CONTINUOUS PRODUCTION OF CELLULOSE ESTERS Roland Clevy, Le Peage-de-Roussillon, and Jean Robin, Roussillon, France, assignors to Societe Rhodiaceta, Paris, France, a body corporate of France Application March 13, 1953, Serial No. 342,214 Claims priority, application France October 29, 1952 4 Claims. (Cl. 260-229) This invention is a continuation-in-part of our copending application Serial No. 330,968, filed on January 13, 1953.

It is an object of the invention to provide a process for the continuous production of cellulose esters, particularly of cellulose acetate. This process is of a socalled homogeneous phase type, that is the esterification is effected in a solvent medium for the ester formed.

This and other objects of the invention will become apparent hereinafter.

According to the invention a process for the continuous production of cellulose esters comprises eliminating the water from a dilute dispersion of cellulose in a large quantity of water, the last stage of this elimination being effected by systematic displacement of the water with a carboxylic acid solvent for the ester being produced, and esterifying continuously the cellulose thus impregnated with acid, without intermediate drying of the said cellulose, by means of an organic acid anhydride in the presence of an esterification catalyst and of a solvent for the cellulose ester using one of the apparatuses described in copending application Serial No. 330,968, filed on l'anuary 13, 1953.

In carrying out the process of the invention one can employ cellulose of any origin; particularly suitable are linters in the form of wads or sheets or wood pulp in the form of flocks or sheets. It is even possible to employ qualities of pulp having a lower percentage content of alpha cellulose than that which is usually required for acetylation. The cellulose employed may also be in the form of compact sheets which defiber badly in anhydrous media or in the presence of small quantities of water.

The cellulose which is used, is defibered in the presence of a large quantity of water, at least 15 times and preferably from 15 to 30 times the weight of the cellulose, in a way such that a dispersion of weak concentration is obtained. For this operation apparatuses may be used such as apparatuses having stirrers or paper mill heaters or any other convenient defibering apparatus.

The entire amount of water present is then eliminated from the dispersion, the last phase of this elimination being efiected continuously by displacement with a carboxylic acid. This displacement is effected in stages, that is to say acid of increasing concentration is used; this permits the use of acid in an amount of from 3 to times the weight of the cellulose. Acid is then removed from the cellulose by any known method in such a way that it contains no more acid than, for example, from 2 to 6 times the weight of the cellulose.

In order to effect this elimination of water any convenient apparatus may be used, such as for example: conveyor belt, vacuum filter, centrifuge or an apparatus in the form of a disc whose base is perforated to allow the elimination of liquids, for example by the action of a vacuum, and which disc rotates about its axis in such a way that various portions thereof pass successively united States Patent 0 "ice der conduits fed with carboxylic acid whose concentration increases from one conduit to the next.

However, particularly favourable results are obtained by using an apparatus analogous to the pulp press of a paper mill. Drainage and pressing by means of pressure rollers and of suction boxes take place on the first part of the wire mesh. The displacement of the remainder of the water with acid is effected later on. For this purpose sprays above pressure rollers which pressure rollers are placed above suction boxes, are used. Each spray is fed with acid from the suction box situated immediately after it, considering the direction of flow of the pulp, the last spray being fed with anhydrous acid. 7

The cellulose impregnated with acid is then comminuted and introduced in continuous manner into an apparatus described in application Serial No. 330,968, filed on January 13, 1953, surrounded by jackets for the circulation of fluids and provided with tubes for leading in reactants near the feed hopper. The esterification is eflected continuously in the apparatus by leading in the esterifying agent continuously and by regulating the temperature of the various portions of the apparatus by circulating water at suitable temperatures in the jackets.

As esterifying agents for carrying out the process it is possible to use all suitable mixtures of an organic acid anhydride, of a catalyst of esterification and of a solvent for the cellulose ester which is obtained by the esterification.

The ester solution which leaves the apparatus may then be treated in any way desired, for example it may be hydrolysed, precipitated, matured, washed or dried.

So that the invention may be better understood the following non-limitative example is given:

Sheets of wood pulp are introduced into a defibering apparatus 1 at the rate of kg. per hour with an excess of water. The defibering is effected at ordinary temperature and the suspension obtained in this way is run into a tub 2 having a stirrer 3 together with a complementary quantity of water to bring the cellulose content of the suspension to 2%. The resulting suspension is then led onto the metallic mesh 4 of a pulp press across which mesh drainage takes place and where the suspension is submitted to the action of several press boxes 5 and suction boxes 6. The water retained by the cellulose sheet is then replaced by acetic acid by the action of sprays 7 and suction boxes 8. The last spray (considering the direction of the movement of the cellulose sheet) is fed with glacial acetic acid and each of the remaining sprays is fed with dilute acetic acid from the suction box immediately following the spray concerned. In this way the quantity of acetic acid'necessary for displacing the water is reduced ,to a minimum, i. e. 3 to 10. times the weight of the cellulose, and the cellulose sheet which has passed underneath the last spray is impregnated with almost anhydrous acetic acid. The resulting cellulose sheet is then pressed without heating between two rollers 9 which may be furnished with a suction system, in such a way that the amount of acetic acid for impregnation isreduced to about twice the weight of the cellulose and the cellulose sheet is then submitted to the action of a comminuting device 10. The cellulose treated in this way together with 300 litres per hour of glacial acetic acid is introduced into the feed hopper of a mixing apparatus 11 of the type described in copending application Serial No. 330,968, filed on January 13, 1953, provided with four jackets 12 and inlet tubes 13 as described above. 870 litres per hour of a mixture consisting of:

Parts by weight Glacial acetic acid 500 Sulphuric acid (66 B.) 9 Acetic anhydride (97%) 360 is introduced continuously into the apparatus 11. Water is circulated in the jackets 12, the water in the first jacket being at 12 C., in the second jacket at 20 C., in the third jacket 40 C. and 55 C. in the fourth jacket, the order of the jackets being taken in the direction of the passage of the reaction mass through the apparatus 11, so that the temperature of the reaction mixture is controlled successively.

The cellulose triacetate solution obtained at the exit of the apparatus 11 through opening 14 is then precipitated, the triacetate separates out and is washed and dried by known means.

The invention has been illustrated by one example showing the production of cellulose triacetate, but the invention is applicable equally to the preparation of other carboxylic esters or mixed carboxylic esters of cellulose, such as for example, cellulose propionate, cellulose butyrate and cellulose acetopropionate.

In the example given the esterification is effected in the presence of an organic acid; with-out going outside the scope of the invention, it is possible to use other solvents for the resulting cellulose ester, for example methylene chloride, instead of an organic acid.

The esterification may be effected at various dilutions depending on the viscosity characteristics and the degree of filtration desired for the final product, the dilution being dependant on the total weight of the reaction mixture and the weight of the cellulose employed.

Although the present invention has been described with particular reference to specific details, it is not intended that such details shall be regarded as limitations upon the scope of the invention except insofar as included in the accompanying claims.

What we claim and desire to secure by Letters Patent 1s:

1. A process for the continuous production of cellulose esters which comprises defibering commercially obtainable dried cellulose in an amount of water corresponding to 15 to 30 times the weight of the cellulose, continuously eliminating said water, the last stage of this elimination being effected continuously by systematic displacement of the water with a lower aliphatic acid solvent for the cellulose ester being produced, and esterifying continuously the cellulose thus impregnated with acid, without intermediate drying, by means of a lower aliphatic acid anhydride in the presence of an esterification catalyst and an organic solvent for the cellulose ester being produced by submitting the reaction mass of cellulose and esterifying agents to a general transfer movement in a predetermined direction and simultaneously to a reciprocating movement directed alternately in the said direction and in direction opposite thereto.

2. A process for the continuous production of cellulose triacctate which comprises defibering commercially ob tainable dried cellulose in an amount of water corresponding to 15 to 30 times the weight of the cellulose, eliminating said water, the last stage of this elimination being citected continuously by systematic displacement with acetic acid in an amount corresponding to from 3 to 10 times the weight of said cellulose, reducing the amount of acetic acid with which said cellulose thus becomes impregnated to from 2 to 6 times the weight of said cellulose, and esterifying continuously the acid im pregnated cellulose, Without intermediate drying, by means of acetic anhydride in the presence of sulphuric acid and glacial acetic acid by submitting the reaction mass of cellulose and esterifying agents to a general transfer movement in a predetermined direction and simultaneously to a reciprocating movement directed alternately in the said direction and in direction opposite thereto.

3. A process for the continuous production of cellulose esters which comprises defibering commercially obtainable dried cellulose in a quantity of water amounting to 15 to 30 times the weight of the cellulose, continuously eliminating said water, the last stage of this elimination being attested by systematic displacement with a lower aliphatic acid solvent for the cellulose ester being pro duced, the amount of said acid used being from 3 to 10 times the weight of said cellulose, and esterifying continuously the cellulose thus impregnated with acid, without intermediate drying of said cellulose, by means of a lower aliphatic acid anhydride in the presence of an esterification catalyst and an organic solvent for the cellulose ester being produced by submitting the reaction mass of cellulose and esterifying agents to a general transfer movement in a predetermined direction and simultaneously to a reciprocating movement directed alternately in the said direction and in direction opposite thereto.

4. A process for the continuous production of cellulose esters which comprises defibering commercially obtainable dried cellulose in an amount of water corresponding to from 15 to 30 times the amount of the cellulose, continuously eliminating said Water, the last stage OK this elimination being effected by systematic displacement with a lower aliphatic acid solvent for the ester being produced, the amount of said acid being from 3 to 10 times the weight of said cellulose, reducing the amount of acid with which said cellulose thus becomes impregnated to from 2 to 6 times the weight of the cellulose, and esterifying continuously the acid impregnated cellulose, without intermediate drying, by means of a lower aliphatic acid anhydride in the presence of an esterification catalyst and an organic solvent for the cellulose ester being produced by submitting the reaction mass of cellulose and esterifying agents to a general transfer movement in a predetermined direction and simultaneously to a reciprocating movement directed alternately in the said direction and in direction opposite thereto.

References Cited in the file of this patent UNITED STATES PATENTS 2,087,263 Olsen July 20, 1937 2,490,754 Hincke Dec. 6, 1949 2,603,635 Seymour July 15, 1952 2,627,515 White Feb. 3, 1953 

1. A PROCESS FOR THE CONTINUOUS PRODUCTION OF CELLULOSE ESTERS WHICH COMPRISES DEFIBERING COMMERCIALLY OBTAINABLE DRIED CELLULOSE IN AN AMOUNT OF WATER CORRESPONDING TO 15 TO 30 TIMES THE WEIGHT OF THE CELLULOSE, CONTINUOUSLY ELIMINATING SAID WATER, THE LAST STAGE OF THIS ELIMINATION BEING EFFECTED CONTINUOUSLY BY SYSTEMATIC DISPLACEMENT OF THE WATER WITH A LOWER ALIPHATIC ACID SOLVENT FOR THE CELLULOSE ESTER BEING PRODUCED, AND ESTERIFYING CONTINUOUSLY THE CELLULOSE THUS IMPREGNATED WITH ACID, WITHOUT INTERMEDIATE DRYING BY MEANS OF A LOWE ALIPHATIC ACID ANHYDRIDE IN THE PRESENCE OF AN ESTERIFICATION CATALYST AND AN ORGANIC SOLVENT FOR THE CELLULOSE ESTER BEING PRODUCED BY SUBMITTING THE REACTION MASS OF CELLULOSE AND ESTERFYING AGENTS TO A GENERAL TRASFER MOVEMENT IN A PREDETERMINED DIRECTION AND SIMULTANEOUSLY TO A RECIPROCATING MOVEMENT DIRECTED ALTERNATELY IN THE SAID DIRECTION AND IN DIRECTION OPPOSITE THERETO. 